1. Field of the Invention
The present invention relates to a keypad, and more particular to a double-layer light guide plate structure having different sizes of light guide plates and a light guide method.
2. Description of Prior Art
In addition to liquid crystal displays, signs, and advertising billboards, backlight modules are also used extensively in electronic products such as mobile phones and personal digital assistants. Since a backlight module is generally installed in a keypad, users can operate the keypad successfully even at nighttime or in a dark environment.
Traditional keypads install a light guide plate inside a keypad structure and a light emitting diode at the periphery or the bottom of the light guide plate. When the electronic product is used, the light emitting diode will be lit immediately, and the emitted light will be guided into the light guide plate. By then, the light guide plate guides the light to the keypad installed at the top of the light guide plate to create a light transmission effect at the surface of the keypad, so that users can see the word, number or symbol on the surface of each key clearly.
Traditional backlights used for keypads produce single-color light only, and color patterns are printed on the keys of a keypad, such that a color light transmission effect can be created at the surface of the keypad. Since the color patterns printed on the keypad requires a process of performing ink printing for several times in order to print the patterns on the keypad, therefore such process consumes much manufacturing time and effort, and the inventor of the present invention discloses a technology as illustrated in FIG. 1 to overcome the foregoing shortcomings. A hollow word 12a or pattern is printed onto each key 11a of a keypad module 1a, and a light guide structure is installed at the bottom of the keypad module 1a. The light guide structure is comprised of a plurality of light guide plates 2a, 2b, 2c, and at least one light guide band 21a, 21b, 21c is formed on a layer of light guide plate 2a, 2b, 2c and disposed at a position corresponding to the key 11a. The light guide bands 21a, 21b, 21c are arranged alternately or stacked on each other, and the light guide band has a color layer 22a, 22b, 22c. If an electronic device controls and selectively lights up each layer of light emitting elements 3a, 3b, 3c one by one, each layer of the light guide bands 21a, 21b, 21c will produce different color lights or mixed color lights which are refracted to the corresponding keys 11a of the keypad module 1a respectively, such that each key 11a will be able to create a light transmission effect with different color lights and show the word, number or pattern on the surface of the keypad.
Although the design of the foregoing light guide structure can provide an effect of a change of color for the multi-color light at the surface of the keypad, yet the thickness and hardness of the light guide structure will be increased. Users may find it difficult to press the key 11a, and need to apply an excessive force to the keys for the operation. As a result, the keys are pressed onto the metal bracket, and the metal bracket is deformed and touched the circuit board, and thus this design of keypad structure requires further improvements.